REDUCTION OF IRON CONTENT IN VERMICULITE
O. A. Vlasov
and E. V. Kulinskaya
Translated from Novye Ogneupory, No. 8, pp. 22 – 25, August 2010.
Original article submitted March 20, 2010.
The possibility is considered of removing iron from vermiculite as a result of treating it with water-containing
gases. As a result it is found that the iron content may be reduced by almost a factor of three. As detected, a re
duction of the iron content of vermiculite leads to a volumetric increase that should be reflected in its heat in
Keywords: vermiculite, iron hydride, chemical analysis, heat insulation properties, expansion.
Vermiculite is a mineral of the hydromica group, formed
from bentonite or phlogopite under the action of hydrother-
mal processes in a weathered core. The main property of ver-
miculite, governing its industrial value, is a capacity to in-
crease in volume rapidly (swell) on firing in the range
400 – 1000°C. The initial volume of a grain increases by a
factor of 20 or more. The material exhibits high heat- and
sound- insulating properties, it is not toxic, not subject to de-
cay, and does not propagate mildew. The unique technical
properties of vermiculite are high stability at elevated tem-
perature and refractoriness, and reflecting capacity.
The Russian Federation has the largest mineral raw ma
terial base of vermiculite in the world. More than fifteen de
posits and 30 ore developments with total reserves, including
predicted amounts of more than 150 million tons, have been
studied. Of the developed vermiculite deposits the mining in
dustry is centered at the Kordov (Murmansk region), Potanin
(Chelyabinsk region), and Inaglin (Yakutia) areas. In recent
years attention has been drawn to the Tatar deposit in the
Krasnoyarsk region. The predicted reserves of the Tatar de
posit are 5.6 million tons.
Visually in a solid mass the color of vermiculite of the
Tatar deposit is brownish-yellowish-green. However, under a
microscope dark, brown of different shade, green honey and
silver-gold particles are seen. Color distribution with respect
o vermiculite particles is uniform or not so. The greatest uni
formity with respect to color is distinguished by the dark-
and light-colored platelets. Apart from these platelets there
are vermiculite platelets with a mixed, spotted color, caused
by presence of dark- and light-colored areas. Distribution of
these areas over the surface of a plate in not uniform or with
a regular arrangement. For example, in the central part of a
plate there is a light, gray or silver color, around concentri-
cally arranged white diffuse bands, and towards the edge
parts the color becomes yellow, honey. Silver parts are some-
times not continuously single-plate, and consists of fine
flakes reminiscent sericite.
On heating there is a change in the color of vermiculite
and plate transparency. The initial change in color, develop-
ing in particles of colored areas of vermiculite, is observed in
the range 250 – 270°C. Most resistant of the red-brown color
of the overall mass recorded at 550 – 580°C. However, indi
vidual particles retain color inhomogeneity due to the sil
ver-grey color of the surface of open bundles, and red-brown
color, retained at the edges (boundaries) adjoining these bun
dles. With a further increase in temperature this color feature
is retained. During heating in an open flame at 900°C ver
miculite acquires a brownish-gray color. In fine platelets of
vermiculite they are translucent, and the most translucent are
plates of honey color. The luster of vermiculite is greasy. At
200°C vermiculite particles become more pure, lustrous, and
their transparency increases considerably, and at 270°C their
transparency is markedly reduced and with a further increase
in temperature it disappears entirely.
The shape of vermiculite particles varies: circular, angu
lar, drawn out or of irregular shape; edges are smooth or
toothed; the surface of platelets is from uniform smooth to
wavy, cracked, as it were crumpled. In individual platelets
there are through holes, forming from intergrowth with other
minerals, or round or channel-shaped depressions with uni
Refractories and Industrial Ceramics Vol. 51, No. 4, 2010
1083-4877/10/5104-0247 © 2010 Springer Science+Business Media, Inc.
Institute of Nonferrous Metals and Materials Science, FGOUVPO
Siberian Federal University, Krasnoyarsk, Russia.